Daylight fluorescent pigments absorb radiation in both the ultraviolet and visible ranges of the spectrum and emit visible light by fluorescence. The emitted light adds to the normal reflected color to give brilliant colors which appear to glow in normal daylight. The effect can be very striking. A fluorescent orange color can be up to three times brighter than a conventional orange color in daylight. This fluorescent coloration is desirable in a variety of products including plastics and inks. However, if the pigment is to be used in an ink, particularly in a thin film, the pigment must be of small particle size. Small particle sizes, particularly those sizes of under 10 microns provide a strong brightly colored ink.
Finely divided colored resins or colored pigments heretofore have been prepared by coloring a resin prepared by a condensation polymerization in advance with a dyestuff and then pulverizing the colored resin to obtain finely divided particles. U.S. Pat. Nos. 2,928,873 and 3,116,256 disclose a process for obtaining colored resin particles where a condensate of an aminotriazine compound and an aromatic monosulfonamide compound with formaldehyde is employed as the substrate resin. The resin is then combined with a dye and then ground; however this results in particles having a size greater than one micron. Indeed, presently available grinding methods generally cannot provide particles having an average particle size lower than 3 to 5 microns. Moreover, grinding to such a particle size is quite expensive.
While water continuous emulsion polymerization of vinyl type monomers is a well known polymerization technique which produces particles in the submicron range, such vinyl monomers do not incorporate fluorescent dyes.
It would be desirable to have fluorescent pigments having an average particle size of 10 or less microns which do not require mechanical grinding to achieve their particle size. Such pigments would find use in graphic arts applications such as textile printing inks, gravure or flexographic printing inks, marker inks, and for fluorescent paints. It is also desirable to have a water based pigment system which contains a pigment possessing excellent water resistance and which does not contain volatile organic solvents.